They are, if they are less expensive than the reproductions made by R.A R.E.
The factory version had relatively small outlets, like about 2.100 inches. R.A.R.E. (Ram Air Restoration Enterprises) makes them in sizes up to 3.00" I believe.
Your car is not a numbers matching restoration, so don't pay too much more than the cost of headers plus shipping.
Q, thats where I was going when I asked what the offer was. Some people swear by the LB manifolds...fit is perfect, usually no problems...But, I can't see them performing as well as a good set of headers on a stout engine.
I'm a hobbyist. Not a professional. Don't be hatin'!